The Houdini part:
Setup: 6 hrs? Most of this time went into getting the whitecaps "right". (Gotta lot to learn.)
Simulation and baking time: something between 4--8 hrs.
Time to render with Mantra: 38 hrs for all three cams.
Cam1: 16 hrs. (288 frames)
Cam2: 12 hrs (72 frames; lots of particle sprites).
Cam3: 10 hrs (84 frames; little less sprites).
The least I could get, without losing too much quality.
Blender's sequencer was then used to create the movie file from EXRs coming out of Houdini, as well as Gimp for the titles.
Note: not every rendered frame was used for the final shot.
This is a first approach towards creating an explosion.
the explosion itself is made with the "Fireball", while the secondary shockwave smok was realized with a particle system, metaballs, isooffset, etc.